Vehicle speed limiter system

ABSTRACT

A vehicle speed limiter system installed on a vehicle includes a detection unit to detect a speed limit value of a road while the vehicle is traveling; a setting unit to set the speed limit value; a limiter unit to limit the vehicle speed, based on the speed limit value; an obtainment unit to obtain a stepping amount on an accelerator pedal; a calculation unit to calculate a parameter depending on the stepping amount in a state where the vehicle speed is being limited by the limiter unit; and a display unit to display information based on the parameter, in a case where a speed limit value newly detected by the detection unit is greater than the speed limit value previously set by the setting unit, before the setting unit sets the speed limit value newly detected.

FIELD

The following disclosure generally relates to a vehicle speed limitersystem.

BACKGROUND

Conventionally, a vehicle speed limiter system has been known thatdetects a speed limit value specified on a road for traveling, based onroad signs and the like, and sets the detected speed limit value on thevehicle to limit the vehicle speed. According to such a vehicle speedlimiter system, even if the driver steps on the accelerator pedal to goover the set speed limit value, the vehicle speed remains below the setspeed limit value, and traveling safety can be maintained.

RELATED-ART DOCUMENTS Patent Documents

-   [Patent Document 1] Japanese Laid-open Patent Publication No.    2006-168593

On the other hand, in a state where the vehicle speed is being limited,in general, the driver may not pay sufficient attention to the steppingamount on the accelerator pedal. Therefore, for example, while thevehicle speed is being limited, if a speed limit value is newly detectedto make the speed limit switch to a higher value, and the steppingamount on the accelerator pedal by the driver happens to be large, theswitching of the speed limit may result in unexpected acceleration ofthe vehicle. Moreover, if there is a preceding vehicle, the likelihoodincreases for the vehicle to collide with the preceding vehicle.

In view of the above, if switching to a new speed limit value increasesthe speed limit value of the vehicle while the vehicle speed is beinglimited, it is desirable to make the driver conscious of the steppingamount on the accelerator pedal before the switching, and if thestepping amount on the accelerator pedal is large, to make the driverrecognize it. This is because if the driver knows in advance that theswitching may accelerate the vehicle, and/or likelihood may increase forthe vehicle to collide with the preceding vehicle, the driver may beable to adjust the stepping amount on the accelerator pedal before theswitching.

Thereupon, it is an object of the disclosure to provide a vehicle speedlimiter system that makes a driver recognize the stepping amount on theaccelerator pedal before switching to a new speed limit value in casethat the switching increases the speed limit of the vehicle while thevehicle speed is being limited.

SUMMARY

According to an aspect of the disclosure, a vehicle speed limitersystem, installed on a vehicle, includes a detection unit configured todetect a speed limit value of a road on which the vehicle is traveling;a setting unit configured to set the speed limit value detected by thedetection unit; a limiter unit configured to limit the vehicle speed ofthe vehicle, based on the speed limit value set by the setting unit; anobtainment unit configured to obtain a stepping amount on an acceleratorpedal of the vehicle; a calculation unit configured to calculate aparameter depending on the stepping amount, by using the stepping amountobtained by the obtainment unit in a state where the vehicle speed ofthe vehicle is being limited by the limiter unit; and a display unitconfigured to display information based on the parameter calculated bythe calculation unit, in a case where a speed limit value newly detectedby the detection unit is greater than the speed limit value previouslyset by the setting unit, before the setting unit sets the speed limitvalue newly detected.

In this way, the vehicle speed limiter system obtains the steppingamount on the accelerator pedal in a state where the vehicle speed ofthe vehicle is being limited, and calculates a parameter depending onthe obtained stepping amount. Therefore, according to the vehicle speedlimiter system, the parameter depending on the stepping amount can beobtained while the vehicle speed is being limited.

Also, if a speed limit value greater than the set speed limit value isnewly detected, the vehicle speed limiter system displays informationbased on the parameter depending on the stepping amount on theaccelerator pedal before setting the newly detected speed limit value.Therefore, the driver can take a look at the information displayed basedon the parameter depending on the stepping amount on the acceleratorpedal, before the speed limit value is increased by switching to thenewly detected speed limit value. Consequently, the driver can recognizethe stepping amount on the accelerator pedal before the switching of thespeed limit value.

According to an aspect of the disclosure, it is possible for the driverto recognize the stepping amount on the accelerator pedal beforeswitching to a new speed limit value in case that the switchingincreases the speed limit of the vehicle while the vehicle speed isbeing limited.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a diagram that illustrates an example of a setting controlsystem;

FIG. 2 is a diagram that illustrates an example of a hardwareconfiguration of an ECU for setting the speed limit;

FIG. 3 is a diagram that illustrates an example of a functionalconfiguration of a pedal-based vehicle speed calculation unit;

FIG. 4 is a diagram that illustrates an example of relevant parametersused when calculating the pedal-based vehicle speed based on thestepping amount on the accelerator pedal;

FIG. 5 is a diagram that illustrates an example of a functionalconfiguration of a UI control unit;

FIGS. 6A-6C are diagrams that illustrate display examples of speeddisplay screens;

FIG. 7 is a diagram that illustrates display examples of a speed displayscreen in traveling scenes;

FIG. 8 is a flowchart that illustrates a flow of a process to displaythe pedal-based vehicle speed;

FIG. 9 is a diagram that illustrates an example of a functionalconfiguration of a UI control unit;

FIG. 10 is a diagram that illustrates display examples of a speeddisplay screen in traveling scenes;

FIG. 11 is a diagram that illustrates display examples of a speeddisplay screen in traveling scenes;

FIG. 12 is a diagram that illustrates another display example of a speeddisplay screen;

FIG. 13 is a part of a flowchart that illustrates a flow of a process todisplay the pedal-based vehicle speed;

FIG. 14 is another part of the flowchart that illustrates the flow of aprocess to display the pedal-based vehicle speed;

FIGS. 15A-15B are flowcharts that illustrate flows of a process todetermine whether the condition for calling attention to acceleration issatisfied, and a process to determine whether the terminating conditionfor calling attention to acceleration is satisfied, respectively;

FIG. 16 is a diagram that illustrates an example of a functionalconfiguration of a UI control unit;

FIG. 17 is a diagram that illustrates display examples of a speeddisplay screen in traveling scenes;

FIG. 18 is a diagram that illustrates another display example of a speeddisplay screen;

FIG. 19 is a part of a flowchart that illustrates a flow of a process todisplay the pedal-based vehicle speed;

FIG. 20 is another part of the flowchart that illustrates the flow of aprocess to display the pedal-based vehicle speed; and

FIGS. 21A-21B are flowcharts that illustrate flows of a process todetermine whether the condition for calling attention to collision issatisfied, and a process to determine whether the terminating conditionfor calling attention to collision is satisfied, respectively.

DESCRIPTION OF EMBODIMENTS

In the following, embodiments will be described with reference to thedrawings. Note that in the specification and the drawings, elements thathave substantially the same functions and configurations are assignedthe same codes, and duplicated description will be omitted.

First Embodiment 1. Configuration of Setting Control System

First, a configuration of a setting control system will be describedthat is a system to set a speed limit value in a vehicle control systemcontrolling the vehicle speed based on the speed limit value. FIG. 1 isa diagram that illustrates an example of such a setting control system.As illustrated in FIG. 1, a setting control system 100 includes animaging device 111, a navigation device 112, a communication device 113,and sensors 114. The setting control system 100 also includes an ECU(Electronic Control Unit) for setting speed limit 120 as an example of acontrol device, and a display unit 131. Note that the setting controlsystem 100 in the present embodiment constitutes a vehicle speed limitersystem that has the setting control system 100 connected with anotherECU 140 connected with an acceleration pedal 141, an engine 142, and thelike.

The imaging device 111 captures an image of a road sign on a road fortraveling (road) while the vehicle is traveling, and transmits thecaptured image information to the ECU for setting the speed limit 120every predetermined frame cycle. The navigation device 112 identifiesthe position of the vehicle while traveling, and transmits positionalinformation representing the identified position and map informationincluding the identified position to the ECU for setting the speed limit120, as navigation information.

The communication device 113 is connected with a network such as theInternet to obtain weather information including weather, atmosphericpressure, and air temperature at the position of the vehicle whiletraveling, and transmits the obtained information to the ECU for settingthe speed limit 120, as network communication information.

The sensors 114 include multiple sensors installed in the vehicle, tomeasure various physical quantities, respectively. The sensors 114includes, for example, a vehicle height sensor to measure the vehicleheight, a wind speed sensor to measure the wind speed around thevehicle, an air temperature sensor to measure the air temperature aroundthe vehicle, and an atmospheric pressure sensor to measure theatmospheric pressure around the vehicle. The sensors 114 also include aweight sensor to measure the weight of the vehicle, an inclinationsensor to measure the inclination of the vehicle, and a raindrop sensorto measure raindrops. Note that the physical quantities measured by therespective sensors included in the sensors 114 are transmitted to theECU for setting the speed limit 120, as sensor information.

The ECU for setting the speed limit 120 has a speed limit settingprogram, a pedal-based vehicle speed calculation program, a UI controlprogram, and the like installed. The ECU for setting the speed limit 120functions as a speed limit setting unit 121, a pedal-based vehicle speedcalculation unit 122, and a UI control unit 123, by executing therespective programs.

The speed limit setting unit 121 detects a speed limit value specifiedon a road sign, based on image information transmitted from the imagingdevice 111, and sets the detected speed limit value as the upper limitspeed value on the other ECU 140. The speed limit setting unit 121temporarily stores the detected speed limit value in the switchingcandidate storage unit 124 as a candidate to be used for switching theupper limit speed value, until the detected speed limit value iseventually set on the other ECU 140 as the upper limit speed value. Notethat a candidate to be used for switching the upper limit speed valuewill be referred to as a “candidate of the speed limit value to beswitched”, in the following.

The pedal-based vehicle speed calculation unit 122 obtains a steppingamount on the acceleration pedal 141 by the driver, from the other ECU140. The pedal-based vehicle speed calculation unit 122 calculates avehicle speed estimated from an obtained stepping amount on theacceleration pedal 141 (referred to as a “pedal-based vehicle speed”below). The pedal-based vehicle speed calculated by the estimation is aparameter that directly corresponds to the stepping amount on theacceleration pedal 141, namely, corresponds to the vehicle speed thatwould be obtained assuming that the vehicle speed is not limited by theother ECU 140 even though the vehicle speed is being limited actually.Note that the pedal-based vehicle speed calculation unit 122 uses theimage information, the navigation information, the network communicationinformation, the sensor information, and the like, to calculate thepedal-based vehicle speed.

The UI control unit 123 displays the current vehicle speed included inother ECU information received from the other ECU 140 (referred to asthe “current vehicle speed” below), and the pedal-based vehicle speedcalculated by the pedal-based vehicle speed calculation unit 122 on thedisplay unit 131. This makes it possible for the driver to recognize theparameter (the pedal-based vehicle speed) that corresponds to thestepping amount on the acceleration pedal 141 by himself/herself.

The display unit 131 displays the current vehicle speed and thepedal-based vehicle speed output by the ECU for setting the speed limit120 on a speed display screen.

The other ECU 140 controls, for example, the rotational speed of theengine 142 and the like to limit the vehicle speed, based on the speedlimit value set by the ECU for setting the speed limit 120 as the upperlimit speed value, the stepping amount on the acceleration pedal 141,and the like. Also, in addition to limiting the vehicle speed, the otherECU 140 transmits the other ECU information that includes the currentvehicle speed, the stepping amount on the acceleration pedal 141 of thevehicle, and the accumulated value of the travel distance of thevehicle, to the ECU for setting the speed limit 120.

Note that the example in FIG. 1 is configured to have the imaging device111, the navigation device 112, the communication device 113, and thesensors 114 connected with the ECU for setting the speed limit 120, toinput various information items from these devices into the ECU forsetting the speed limit 120. However, these devices may be connectedwith the other ECU 140 to input various information items from thesedevices into the ECU for setting the speed limit 120 via the other ECU140.

Also, in the example in FIG. 1, the ECU for setting the speed limit 120is provided as an ECU separate from the other ECU 140. However,functions implemented by the ECU for setting the speed limit 120 may beimplemented, for example, on the other ECU 140, so that the ECU forsetting the speed limit 120 is integrated with the other ECU 140.

2. Hardware Configuration of ECU for Setting the Speed Limit

Next, a hardware configuration of the ECU for setting the speed limit120, will be described. FIG. 2 is a diagram that illustrates an exampleof a hardware configuration of the ECU for setting the speed limit 120.

As illustrated in FIG. 2, the ECU for setting the speed limit 120includes a CPU (Central Processing Unit) 201, a RAM (Random AccessMemory) 202, a connection unit 203, and a ROM (Read-Only Memory) 204.Note that these units of the ECU for setting the speed limit 120 aremutually connected via a bus 205.

The CPU 201 is a computer that executes programs (the speed limitsetting program, the pedal-based vehicle speed calculation program, theUI control program, etc.) stored in the ROM 204.

The RAM 202 is a main memory unit such as a DRAM (Dynamic Random AccessMemory) and a SRAM (Static Random Access Memory). The RAM 202 functionsas a work area in which a program stored in the ROM 204 is loaded andexecuted by the CPU 201. The RAM 202 also functions as a storage area inwhich information is temporarily stored that is generated by a programstored in the ROM 204, and executed by the CPU 201 (for example, acandidate of the speed limit value to be switched).

The connection unit 203 is connected with and various devices such asthe imaging device 111 and the navigation device 112, and serves as aninterface to transmit/receive various information items to/from thevarious devices.

The ROM 204 is a main memory unit such as an EPROM and an EEPROM, andstores the programs (the speed limit setting program, the pedal-basedvehicle speed calculation program, the UI control program, etc.)executed by the CPU 201, and information that is used when the programsare executed.

3. Functional Configuration of ECU for Setting the Speed Limit

Next, among functional units implemented by the ECU for setting thespeed limit 120, the pedal-based vehicle speed calculation unit 122 andthe UI control unit 123 will be further described in detail.

3.1 Functions of Pedal-Based Vehicle Speed Calculation Unit

First, functions of the pedal-based vehicle speed calculation unit 122will be described in detail. FIG. 3 is a diagram that illustrates anexample of a functional configuration of the pedal-based vehicle speedcalculation unit 122. As illustrated in FIG. 3, the pedal-based vehiclespeed calculation unit 122 includes an obtainment unit for the steppingamount on the acceleration pedal 301, a calculation unit for thereaction force on the drive system 302, a calculation unit for the airresistance force 303, a calculation unit for the gravity 304, acalculation unit for the frictional force on the road surface 305, andan estimation unit 306.

The obtainment unit for the stepping amount on the acceleration pedal301 obtains a stepping amount on the acceleration pedal 141 by thedriver from the other ECU 140. Note that the vehicle travels by adriving force generated by the driver stepping on the acceleration pedal141 (driving force depending on the stepping amount), and the vehiclespeed while traveling is determined by a balance between the drivingforce and forces reacting against the driving force.

The forces reacting against the driving force includes, for example,reaction force on the drive system, air resistance force, gravity, andfrictional force on the road surface. The pedal-based vehicle speedcalculation unit 122 calculates these forces to calculate thepedal-based vehicle speed. Note that relevant parameters used forcalculating the reaction force on the drive system, the air resistanceforce, the gravity, the frictional force on the road surface, and thelike are as illustrated in FIG. 4. In the following, with reference toFIG. 4, functions will be described for the calculation unit for thereaction force on the drive system 302, the calculation unit for the airresistance force 303, the calculation unit for the gravity 304, and thecalculation unit for the frictional force on the road surface 305.

The calculation unit for the reaction force on the drive system 302calculates the reaction force on the drive system generated on the drivesystem of the vehicle. The reaction force on the drive system of thevehicle can be represented by a function of the vehicle weight, and canbe calculated by obtaining the vehicle weight. As illustrated in FIG. 4,as the vehicle weight, for example, a measurement result measured by aweight sensor may be used. Alternatively, a subduction amount of thevehicle body may be calculated based on a measurement result measured bya vehicle height sensor, to estimate the vehicle weight based on thecalculated subduction amount. Note that the subduction amount of thevehicle body may be calculated by analyzing image information capturedby the imaging device 111, instead of a measurement result by thevehicle height sensor.

The calculation unit for the air resistance force 303 calculates the airresistance force against the vehicle. The air resistance force can berepresented by a function of the vehicle shape, the wind speed, and theair density, and can be calculated by obtaining the vehicle shape, thewind speed, and the air density. As illustrated in FIG. 4, the vehicleshape is assumed to be stored in advance in the speed limit setting unit121 of the ECU for setting the speed limit 120. Also, the wind speed canbe derived based on, for example, positional information of vehicle, andweather information based on the positional information of the vehicle.Alternatively, a measurement result measured by a wind speed sensor maybe used.

Note that positional information of the vehicle can be obtained fromnavigation information transmitted from the navigation device 112, andweather information can be obtained from network communicationinformation transmitted from the communication device 113.

Also, the air density can be calculated based on air temperatureinformation and atmospheric pressure information. The air temperatureinformation can be derived based on, for example, the positionalinformation of the vehicle and weather information based on thepositional information of the vehicle. Alternatively, a measurementresult measured by an air temperature sensor may be used.

Also, the atmospheric pressure information can be derived based on, forexample, the positional information of the vehicle and weatherinformation based on the positional information of the vehicle.Alternatively, a measurement result measured by an atmospheric pressuresensor may be used.

The calculation unit for the gravity 304 calculates gravity acting onthe vehicle. The gravity can be represented by a function of the vehicleweight and the road surface gradient, and can be calculated by obtainingthe vehicle weight and the road surface gradient. As illustrated in FIG.4, as the vehicle weight, for example, a measurement result measured bya weight sensor may be used. Alternatively, a subduction amount of thevehicle body may be calculated based on a measurement result measured bya vehicle height sensor, to estimate the vehicle weight based on thecalculated subduction amount. Note that the subduction amount of thevehicle body may be calculated by analyzing image information capturedby the imaging device 111, instead of a measurement result by thevehicle height sensor.

Also, as the road surface gradient, for example, a measurement resultmeasured by a gradient sensor may be used. Alternatively, it may becalculated by analyzing image information transmitted from the imagingdevice 111. Alternatively, it may be derived based on the positionalinformation of the vehicle and weather information based on thepositional information of the vehicle. Note that the positionalinformation of the vehicle and map information can be obtained fromnavigation information transmitted from the navigation device 112.

The calculation unit for the frictional force on the road surface 305calculates the friction force that acts on the vehicle whose tires arein contact with the road surface. The frictional force on the roadsurface can be represented by a function of rain information and tireabrasion information, and can be calculated by obtaining the raininformation and the tire abrasion information. As illustrated in FIG. 4,as rain information, for example, a measurement result measured by araindrop sensor may be used. Alternatively, it may be derived based onthe positional information of the vehicle and weather information basedon the positional information of the vehicle.

Also, the tire abrasion information can be estimated based on, forexample, the accumulated value of the travel distance of the vehicle.Note that the accumulated value of the travel distance of the vehiclecan be obtained from the other ECU information transmitted from theother ECU 140.

The estimation unit 306 calculates the pedal-based vehicle speed, basedon the driving force depending on the stepping amount obtained by theobtainment unit for the stepping amount on the acceleration pedal 301,the reaction force on the drive system, the air resistance force, thegravity, and the frictional force on the road surface that arecalculated as the forces reacting against the driving force.

3.2 Functions of UI Control Unit

Next, functions of the UI control unit 123 will be described. FIG. 5 isa diagram that illustrates a functional configuration of the UI controlunit 123. As illustrated in FIG. 5, the UI control unit 123 includes acurrent vehicle speed display unit 501, and a pedal-based vehicle speeddisplay unit 502.

The current vehicle speed display unit 501 extracts a current vehiclespeed of the vehicle from the other ECU information transmitted from theother ECU 140, and displays the extracted current vehicle speed on aspeed display screen of the display unit 131.

The pedal-based vehicle speed display unit 502 displays a pedal-basedvehicle speed calculated by the estimation unit 306 of the pedal-basedvehicle speed calculation unit 122, on a speed display screen of thedisplay unit 131.

4. Display Examples of Speed Display Screens

Next, speed display screens displayed on the display unit 131 by the UIcontrol unit 123 will be described. FIGS. 6A-6C are diagrams thatillustrate display examples of speed display screens. Among these, FIG.6A illustrates a speed display screen 600 that displays the currentvehicle speed and the pedal-based vehicle speed by indicator hands 601and 602, respectively, with respect to speed values arrayed around adial.

In FIG. 6A, the indicator hand 601 indicates the current vehicle speed.Also, the indicator hand 602 indicates the pedal-based vehicle speed.Note that in the example in FIG. 6A, the pedal-based vehicle speed is“100 km/h”, whereas the current vehicle speed is “60 km/h”. This isbecause “60 km/h” is set as the upper limit speed value, and the currentvehicle speed is limited to be less than or equal to “60 km/h”.

FIG. 6B illustrates speed display screens 600 that digitally display thecurrent vehicle speed and the pedal-based vehicle speed. In an examplein FIG. 6B, the current vehicle speed display area 611 shows “60 km/h”as the current vehicle speed, and the pedal-based vehicle speed displayarea 612 shows “100 km/h” as the pedal-based vehicle speed.

Note that the pedal-based vehicle speed shown in the pedal-based vehiclespeed display area may be the difference from the current vehicle speed.The right side of FIG. 6B illustrates a case where the difference fromthe current vehicle speed is shown as the pedal-based vehicle speed inthe pedal-based vehicle speed display area 612. The current vehiclespeed of “60 km/h” and the pedal-based vehicle speed of “100 km/h”result in the difference of “+40 km/h”.

FIG. 6C illustrates another speed display screen 600 that shows thecurrent vehicle speed and the pedal-based vehicle speed by bar graphs621 and 622, respectively, with respect to speed values arrayedlinearly. In FIG. 6C, the bar graph 621 indicates the current vehiclespeed. Also, the bar graph 622 indicates the pedal-based vehicle speed.

5. Display Examples of Speed Display Screen in Traveling Scenes

Next, display examples of a speed display screen in traveling sceneswill be described. FIG. 7 is a diagram that illustrates display examplesof one of the speed display screens 600 in traveling scenes.

Specifically, the figure illustrates display examples of the speeddisplay screen 600 in traveling scenes in a case where travelling hasbeen started in state where a speed limit value 711 of “60 km/h” hasbeen detected based on a road sign 701, and an upper limit speed valueof “60 km/h” has been set in the other ECU 140.

As illustrated in FIG. 7, when the current vehicle speed is less thanthe upper limit speed value of “60 km/h”, the current vehicle speed 721is equivalent to the pedal-based vehicle speed 722. In other words, whenthe current vehicle speed is less than the upper limit speed value of“60 km/h”, the current vehicle speed 721 changes following the steppingamount on the acceleration pedal 141 by the driver.

On the other hand, once the current vehicle speed reaches the upperlimit speed value of “60 km/h”, the current vehicle speed 721 remainsunchanged at the upper limit speed value of “60 km/h” irrespective ofthe pedal-based vehicle speed 722. Therefore, the current vehicle speedof “60 km/h” is displayed, and the pedal-based vehicle speed of “100km/h” is displayed on the speed display screen 600, for example, at timeT1.

Note that in the example in FIG. 7, at time T1, another speed limitvalue is detected based on a road sign 702, and “80 km/h” is stored as acandidate of the speed limit value to be switched. Then, when thevehicle passes by the position where the road sign 702 is installed, thecandidate of the speed limit value to be switched is transmitted to theother ECU 140, to be set in the other ECU 140, and the upper limit speedvalue is switched.

Once the upper limit speed value is switched, the vehicle speed may beincreased depending on the stepping amount on the acceleration pedal141. In this case, since the pedal-based vehicle speed has been alreadydisplayed on the speed display screen 600, the driver can recognize thestepping amount on the acceleration pedal 141 by himself/herself on thespeed display screen 600 before the vehicle passes by the position wherethe road sign 702 is installed. Thus, the driver can adjust the steppingamount on the acceleration pedal 141.

Specifically, if the driver judges that behavior of the vehicle maychange (the vehicle accelerates steeply) by the switching of the upperlimit speed value because the pedal-based vehicle speed is high, thedriver can decrease in advance the stepping amount on the accelerationpedal 141, to avoid steep acceleration of the vehicle and to maintainsafe traveling. Note that the driver can confirm that he/she hasdecreased the stepping amount on the acceleration pedal 141 by thedecreased pedal-based vehicle speed. A speed display screen 600 at timeT2 illustrates a state when the stepping amount on the accelerationpedal 141 is decreased. After the switching of the upper limit speedvalue, the current vehicle speed 721 increases gradually.

After the switching of the upper limit speed value, the current vehiclespeed 721 increases gradually, and reaches “80 km/h”. which is the upperlimit speed value after the switching. After that, the current vehiclespeed 721 remains unchanged at the upper limit speed value of “80 km/h”irrespective of the pedal-based vehicle speed 722. Therefore, thecurrent vehicle speed of “80 km/h” is displayed, and the pedal-basedvehicle speed of “87 km/h” is displayed on the speed display screen 600,for example, at time T3. Similarly, the current vehicle speed of “80km/h” is displayed, and the pedal-based vehicle speed of “110 km/h” isdisplayed on the speed display screen 600, for example, at time T4.

In this way, in the embodiment, even in a state where the vehicle speedis being limited to be less than or equal to the speed limit value dueto the vehicle speed limit based on the speed limit value, thepedal-based vehicle speed is displayed on the speed display screen 600for scenes. Therefore, even in a state where the vehicle speed is beinglimited to be less than the speed limit value, the driver can recognizethe stepping amount on the acceleration pedal 141 by himself/herself,and can adjust the stepping amount if necessary.

6. Flow of Process to Display the Pedal-Based Vehicle Speed

Next, a flow of a process to display the pedal-based vehicle speed bythe ECU for setting the speed limit 120, will be described. FIG. 8 is aflowchart that illustrates a flow of the process to display thepedal-based vehicle speed by the ECU for setting the speed limit 120.Upon an activation of the vehicle speed limiter system, the process todisplay the pedal-based vehicle speed illustrated in FIG. 8 is started,and executed every predetermined cycle (for example, a cyclesynchronized with a frame cycle).

At Step S801, the current vehicle speed display unit 501 of the UIcontrol unit 123 obtains the current vehicle speed from the other ECU140, and displays the current vehicle speed on the speed display screen600. At Step S802, the estimation unit 306 of the pedal-based vehiclespeed calculation unit 122 calculates the pedal-based vehicle speed, andindicates the calculation result to the UI control unit 123. Also, thepedal-based vehicle speed display unit 502 of the UI control unit 123displays the pedal-based vehicle speed on the speed display screen 600.

At Step S803, the speed limit setting unit 121 determines whether thespeed limit value has been detected. At Step S803, if determining thatthe speed limit value has been detected, the speed limit setting unit121 goes forward to Step S804. At Step S804, the speed limit settingunit 121 stores the detected speed limit value in the switchingcandidate storage unit 124 as a candidate of the speed limit value to beswitched.

On the other hand, at Step S803, if determining that the speed limitvalue has not been detected, the speed limit setting unit 121 goesforward to Step S805.

At Step S805, the speed limit setting unit 121 determines whether acandidate of the speed limit value to be switched has been stored in theswitching candidate storage unit 124. At Step S805, if determining thatit has not been stored, the speed limit setting unit 121 goes forward toStep S809.

On the other hand, if determining at Step S805 that it has been stored,the speed limit setting unit 121 determines that it is before passingthe installed position of the road sign, and goes forward to Step S806.Note that a circumstance where a speed limit value is not detected, buta candidate of the speed limit value to be switched has been stored, maybe caused, for example, by unsuccessful detection of a speed limit valuefrom a specific frame of image information, for some reason, amongframes of image information transmitted every predetermined frame cycle.This is because multiple frames of image information are received aftera speed limit value has been first detected until the vehicle passes bythe installed position of the road sign, and it is possible that some ofthe frames may include image information from which the speed limitvalue cannot be detected.

At Step S806, the speed limit setting unit 121 determines whether thevehicle has passed by the installed position of the road sign specifyingthe detected speed limit value. At Step S806, if determining that thevehicle has not yet passed it by, the speed limit setting unit 121 goesforward to Step S809.

On the other hand, at Step S806, if determining that the vehicle haspassed it by, the speed limit setting unit 121 goes forward to StepS807. At Step S807, the speed limit setting unit 121 transmits thecandidate of the speed limit value to be switched that has been storedin the switching candidate storage unit 124 to the other ECU 140, andissues a command to set it as the upper limit speed value.

At Step S808, the speed limit setting unit 121 deletes the candidate ofthe speed limit value to be switched stored in the switching candidatestorage unit 124.

At Step S809, the UI control unit 123 determines whether it has receivedan end command of the process to display the pedal-based vehicle speed.If determining that it has not received an end command, the UI controlunit 123 goes back to Step S801. On the other hand, if the vehicle speedlimiter system has stopped, the UI control unit 123 determines that ithas received an end command, and terminates the process to display thepedal-based vehicle speed.

7. Summary

As clarified by the above description, the ECU for setting the speedlimit 120 according to the embodiment is configured

to obtain the stepping amount on the accelerator pedal by the driver ina state where the vehicle speed of the vehicle is being limited,

to calculate the driving force of the vehicle calculated based on theobtained stepping amount, and the forces reacting against the drivingforce, so as to estimate the vehicle speed supposed to be directlyobtained by the stepping amount, as the pedal-based vehicle speed, and

to display the estimated pedal-based vehicle speed on the speed displayscreen along with the current vehicle speed.

Thus, in a state where the vehicle speed is being limited to be lessthan the speed limit value, the driver can recognize the stepping amounton the acceleration pedal by himself/herself.

Consequently, the driver can judge by himself/herself whether there is alikelihood that the vehicle accelerates steeply due to the switching ofthe speed limit value. Also, the driver can adjust the stepping amounton the accelerator pedal before the speed limit value is switched, andsafe traveling of the vehicle can be maintained when the speed limitvalue is switched.

Second Embodiment

The first embodiment is configured to display the pedal-based vehiclespeed so that the driver can recognize the stepping amount on theaccelerator pedal, and can judge by himself/herself whether behavior ofthe vehicle may change (the vehicle accelerates steeply) by theswitching of the speed limit value. In contrast to this, in the secondembodiment, a UI control unit determines whether the vehicle acceleratessteeply by the switching of the speed limit value. Also, if determiningthat there is a likelihood that the vehicle accelerates steeply, the UIcontrol unit displays a message for calling attention of the driver. Inthe following, the second embodiment will be described in detail,focusing on different points from the first embodiment.

1. Functions of UI Control Unit

First, functions of the UI control unit 900 will be described accordingto the embodiment. FIG. 9 is a diagram that illustrates a functionalconfiguration of the UI control unit 900. As illustrated in FIG. 9, theUI control unit 900 includes a current vehicle speed display unit 501, apedal-based vehicle speed display unit 502, a determination unit 901,and a message output unit 902. Among these, the current vehicle speeddisplay unit 501 and the pedal-based vehicle speed display unit 502 havebeen described in the first embodiment, and their description is omittedhere.

The determination unit 901 determines whether there is a likelihood thatthe vehicle accelerates steeply when the speed limit setting unit 121has set a candidate of the speed limit value to be switched in the otherECU 140, and switches the upper limit speed value. If determining thatthere is a likelihood of steep acceleration, the determination unit 901issues a command to the message output unit 902 to display a “messagefor calling attention to acceleration”.

The determination unit 901 determines whether there is a likelihood ofsteep acceleration, based on the speed limit value currently set, thecandidate of the speed limit value to be switched, the current vehiclespeed, and the pedal-based vehicle speed, by determining whether all ofthe following items of the “condition for calling attention toacceleration” are satisfied:

the current vehicle speed is equivalent to the speed limit valuecurrently set;

the current pedal-based vehicle speed is greater than the currentvehicle speed;

the difference between the candidate of the speed limit value to beswitched and the speed limit value currently set is greater than orequal to a predetermined threshold; and

the current pedal-based vehicle speed is greater than the candidate ofthe speed limit value to be switched.

Then, if determining that the condition for calling attention toacceleration is satisfied, the determination unit 901 issues a commandto the message output unit 902 to display the “message for callingattention to acceleration”.

Furthermore, in a state where the message for calling attention toacceleration is being displayed, once the candidate of the speed limitvalue to be switched is transmitted to the other ECU 140, and the upperlimit speed value is switched, the determination unit 901 determineswhether it is a timing to stop displaying the message for callingattention to acceleration, and issues a command to the message outputunit 902. Specifically, the determination unit 901 issues a command tothe message output unit 902 to stop displaying the “message for callingattention to acceleration” if determining that one of the followingitems of the “terminating condition for the message for callingattention to acceleration” is satisfied:

the current pedal-based vehicle speed is less than or equal to the newlyset speed limit value; and

the current vehicle speed has reached the newly set speed limit value.

In response to a command to display the “message for calling attentionto acceleration” from the determination unit 901, the message outputunit 902 displays a predetermined message for calling attention toacceleration on the speed display screen 600. Also, in response to acommand to stop displaying the “message for calling attention toacceleration” from the determination unit 901, the message output unit902 stops displaying the message for calling attention to acceleration.

2. Display Examples of Speed Display Screen in Traveling Scenes

Next, display examples of the speed display screen 600 in travelingscenes will be described. FIG. 10 is a diagram that illustrates displayexamples of the speed display screen 600 in traveling scenes.

Specifically, the figure illustrates display examples of the speeddisplay screen 600 in traveling scenes in a case where travelling hasbeen started in state where a speed limit value 711 of “60 km/h” hasbeen detected based on a road sign 701, and an upper limit speed valueof “60 km/h” has been set in the other ECU 140.

As illustrated in FIG. 10, the speed limit setting unit 121 detects aspeed limit value based on a road sign 702 at time T1, and stores acandidate of the speed limit value to be switched in the switchingcandidate storage unit 124. Once the speed limit setting unit 121 storesthe candidate of the speed limit value to be switched, the determinationunit 901 determines whether there is a likelihood that the vehicleaccelerates steeply by determining whether the condition for callingattention to acceleration is satisfied.

At time T1, the determination unit 901 determines that the condition forcalling attention to acceleration is satisfied because

the current vehicle speed 721=“60 km/h” is equivalent to the speed limitvalue currently set 711=“60 km/h”;

the current pedal-based vehicle speed 722=“100 km/h” is greater than thecurrent vehicle speed 721=“60 km/h”;

the difference=“20 km/h” between the candidate of the speed limit valueto be switched=“80 km/h” and the speed limit value currently set 711=“60km/h” is greater than or equal to a predetermined threshold; and

the current pedal-based vehicle speed 722=“100 km/h” is greater than thecandidate of the speed limit value to be switched=“80 km/h”.Consequently, the message for calling attention to acceleration 1040 isdisplayed on the speed display screen 600.

Also, as illustrated in FIG. 10, at time T2, the vehicle passes by theposition where the road sign 702 is installed. When the vehicle passesby the position where the road sign 702 is installed, the speed limitsetting unit 121 transmits the candidate of the speed limit value to beswitched to the other ECU 140, and issues a command to set it as theupper limit speed value. Thus, the candidate of the speed limit value tobe switched (“80 km/h”) is set, and the upper limit speed value isswitched.

After the upper limit speed value has been switched by the candidate ofthe speed limit value to be switched (=“80 km/h”), the message forcalling attention to acceleration is displayed on the speed displayscreen 600 until the terminating condition for the message for callingattention to acceleration is satisfied.

At time T2, the determination unit 901 determines that the terminatingcondition for the message for calling attention to acceleration is notsatisfied because

the current pedal-based vehicle speed 722=“87 km/h” is not less than orequal to the newly set speed limit value=“80 km/h”; and

the current vehicle speed 721=“60 km/h” does not reach the newly setspeed limit value=“80 km/h”. Consequently, displaying the message forcalling attention to acceleration 1040 on the speed display screen 600continues.

Similarly, at time T3, the determination unit 901 determines that theterminating condition for the message for calling attention toacceleration is not satisfied because

the current pedal-based vehicle speed 722=“87 km/h” is not less than orequal to the newly set speed limit value=“80 km/h”; and

the current vehicle speed 721=“72 km/h” does not reach the newly setspeed limit value=“80 km/h”. Consequently, displaying the message forcalling attention to acceleration 1040 on the speed display screen 600continues.

On the other hand, at time T4, the determination unit 901 determinesthat the terminating condition for the message for calling attention toacceleration is satisfied because

the current vehicle speed 721=“80 km/h” has reached the newly set speedlimit value (=“80 km/h”). Consequently, displaying the message forcalling attention to acceleration 1040 on the speed display screen 600ends.

3. Other Display Examples of Speed Display Screen in Traveling Scenes

Next, other display examples of the speed display screen 600 intraveling scenes will be described. FIG. 11 is a diagram thatillustrates other display examples of the speed display screen 600 intraveling scenes. FIG. 10 illustrates a case where the condition forcalling attention to acceleration is satisfied, whereas FIG. 11illustrates a case where the condition for calling attention toacceleration is not satisfied.

At time T1, the determination unit 901 determines that the condition forcalling attention to acceleration is not satisfied because

the current pedal-based vehicle speed 1102=“78 km/h” is less than thecandidate of the speed limit value to be switched=“80 km/h”.Consequently, the message for calling attention to acceleration is notdisplayed on the speed display screen 600.

In the example in FIG. 11, the state determined that the condition forcalling attention to acceleration is not satisfied continues until thevehicle passes by the position where the road sign 702 is installed.Therefore, the vehicle will not accelerate steeply even if the candidateof the speed limit value to be switched (=“80 km/h”) is set, and theupper limit speed value is switched. Therefore, there is no need todisplay the message for calling attention to acceleration.

Consequently, in the example in FIG. 11, the message for callingattention to acceleration is not displayed before and after theswitching of the upper limit speed value, and after the switching, thecurrent vehicle speed 1101 approaches the pedal-based vehicle speed 1102(see time T2). Then, at time T3, the current vehicle speed 1101 becomesequivalent to the pedal-based vehicle speed 1102.

Note that if the current pedal-based vehicle speed 1102 is less than thecandidate of the speed limit value to be switched as in the example inFIG. 11, another message may be displayed, for example, as in FIG. 12.FIG. 12 is a diagram that illustrates another display example of thespeed display screen 600, and includes an example of a message 1202 tobe displayed on the speed display screen 600 if the current pedal-basedvehicle speed 1102 is less than the candidate of the speed limit valueto be switched.

As illustrated in FIG. 12, by indicating to the driver that thepedal-based vehicle speed 1102 has a margin for the upper limit speedvalue upon the switching of the upper limit speed value, the driver canrecognize that he/she may increase the stepping amount on theacceleration pedal 141.

Note that the example in FIG. 12 includes yet another indicator hand1201 to indicate the candidate of the speed limit value to be switched.Thus, if the upper limit speed value is switched, the driver can easilyrecognize how much margin is allowed for the pedal-based vehicle speed1102 with respect to the upper limit speed value after the switching.

4. Flow of Process to Display the Pedal-Based Vehicle Speed

Next, a flow of a process to display the pedal-based vehicle speed bythe ECU for setting the speed limit 120, will be described. FIG. 13 andFIG. 14 constitute a flowchart that illustrates a flow of a process todisplay the pedal-based vehicle speed by the ECU for setting the speedlimit 120. Upon an activation of the vehicle speed limiter system, theprocess to display the pedal-based vehicle speed illustrated in FIG. 13and FIG. 14 is started, and executed every predetermined cycle (forexample, a cycle synchronized with a frame cycle). Note thatsubstantially the same steps as the steps in the process to display thepedal-based vehicle speed illustrated in FIG. 8 are assigned the samereference numbers, and their description is omitted here. Steps S1301 toS1305 in FIG. 13 and Steps S1401 to S1405 in FIG. 14 are different fromFIG. 8.

At Step S1301, the determination unit 901 of the UI control unit 900obtains a speed limit value that has been detected by the speed limitsetting unit 121 and has already been set as the upper limit speed valuein the other ECU 140.

At Step S1302, the determination unit 901 of the UI control unit 900determines whether the candidate of the speed limit value to be switchedis greater than the speed limit value currently set. At Step S1302, ifdetermining that the candidate of the speed limit value to be switchedis greater than the speed limit value currently set, the determinationunit 901 determines that the upper limit speed value will increase bythe switching, and goes forward to Step S1303.

At Step S1303, the determination unit 901 of the UI control unit 900determines whether the condition for calling attention to accelerationis satisfied. Note that a process to determine whether the condition forcalling attention to acceleration is satisfied that is executed by thedetermination unit 901 of the UI control unit 900, will be described indetail later.

As a result of the process to determine whether the condition forcalling attention to acceleration is satisfied, if determining that thecondition for calling attention to acceleration is satisfied, thedetermination unit 901 goes forward to Step S1305 from Step S1304. AtStep S1305, the message output unit 902 of the UI control unit 900displays the message for calling attention to acceleration. After that,the determination unit 901 goes forward to Step S806 in FIG. 14.

On the other hand, at Step S1302, if determining that the candidate ofthe speed limit value to be switched is less than or equal to the speedlimit value currently set, or if determining at Step S1304 that thecondition for calling attention to acceleration is not satisfied, thedetermination unit 901 goes directly forward to Step S806 in FIG. 14.

At Step S1401 in FIG. 14, the determination unit 901 of the UI controlunit 900 determines whether the message for calling attention toacceleration is currently displayed. If determining that the message forcalling attention to acceleration is not displayed, the determinationunit 901 goes forward to Step S809. On the other hand, the message forcalling attention to acceleration is currently displayed, thedetermination unit 901 goes forward to Step S1402.

At Step S1402, the determination unit 901 of the UI control unit 900determines whether the terminating condition for the message for callingattention to acceleration is satisfied. Note that a process to determinewhether the terminating condition for the message for calling attentionto acceleration is satisfied will be described in detail later.

As a result of determination at Step S1402, if determining that theterminating condition for the message for calling attention toacceleration is satisfied, the determination unit 901 goes forward toStep S1404 from Step S1403. At Step S1404, the determination unit 901 ofthe UI control unit 900 deletes the candidate of the speed limit valueto be switched from the switching candidate storage unit 124. Thus,displaying the message for calling attention to acceleration endsthereafter.

On the other hand, if determining that the terminating condition for themessage for calling attention to acceleration is not satisfied, thedetermination unit 901 goes forward to Step S1405 from Step S1403. AtStep S1405, the determination unit 901 of the UI control unit 900 issuesa command to display the message for calling attention to acceleration.Thus, the message output unit 902 of the UI control unit 900 continuesto display the message for calling attention to acceleration.

5. Details of Process to Determine Whether the Condition for CallingAttention to Acceleration is Satisfied

Next, the process to determine whether the condition for callingattention to acceleration is satisfied (Step S1303) in the process todisplay the pedal-based vehicle speed, will be described in detail. FIG.15A is a flowchart that illustrates a flow of the process to determinewhether the condition for calling attention to acceleration issatisfied.

At Step S1501, the determination unit 901 of the UI control unit 900determines whether the current vehicle speed is equivalent to the speedlimit value currently set. At Step S1501, if determining that they arenot equivalent, the determination unit 901 goes forward to Step S1506.On the other hand, at Step S1501, if determining that they areequivalent, the determination unit 901 goes forward to goes forward toStep S1502.

At Step S1502, the determination unit 901 of the UI control unit 900determines whether the current pedal-based vehicle speed is greater thanthe current vehicle speed. At Step S1502, if determining that it is notgreater, the determination unit 901 goes forward to Step S1506. On theother hand, at Step S1502, if determining that it is greater, thedetermination unit 901 goes forward to goes forward to Step S1503.

At Step S1503, the determination unit 901 of the UI control unit 900determines whether the difference between the candidate of the speedlimit value to be switched and the speed limit value currently set isgreater than or equal to the predetermined threshold. At Step S1503, ifdetermining that it is less than the predetermined threshold, thedetermination unit 901 goes forward to goes forward to Step S1506. Onthe other hand, if determining that it is greater than or equal to thepredetermined threshold, the determination unit 901 goes forward to goesforward to Step S1504.

At Step S1504, the determination unit 901 of the UI control unit 900determines whether the current pedal-based vehicle speed is greater thanthe candidate of the speed limit value to be switched. At Step S1504, ifdetermining that the current pedal-based vehicle speed is less than orequal to the candidate of the speed limit value to be switched, thedetermination unit 901 goes forward to goes forward to Step S1506. Onthe other hand, if determining that the current pedal-based vehiclespeed is greater than the candidate of the speed limit value to beswitched, the determination unit 901 goes forward to goes forward toStep S1505.

At Step S1505, the determination unit 901 of the UI control unit 900determines that the condition for calling attention to acceleration issatisfied, and goes back to Step S1304 in FIG. 13. Also, at Step S1506,the determination unit 901 of the UI control unit 900 determines thatthe condition for calling attention to acceleration is not satisfied,and goes back to Step S1304 in FIG. 13.

6. Details of Process to Determine Whether the Terminating Condition forCalling Attention to Acceleration is Satisfied

Next, the process to determine whether the terminating condition forcalling attention to acceleration is satisfied (Step S1401) in theprocess to display the pedal-based vehicle speed, will be described indetail. FIG. 15B is a flowchart that illustrates a flow of the processto determine whether the terminating condition for calling attention toacceleration is satisfied.

At Step S1311, the determination unit 901 of the UI control unit 900determines whether the current pedal-based vehicle speed is greater thanthe newly set speed limit value. At Step S1511, if determining that thecurrent pedal-based vehicle speed is less than or equal to the newly setspeed limit value, the determination unit 901 goes forward to StepS1514. On the other hand, at Step S1511, if determining that the currentpedal-based vehicle speed is greater than the newly set speed limitvalue, the determination unit 901 goes forward to Step S1512.

At Step S1512, the determination unit 901 of the UI control unit 900determines whether the current vehicle speed has reached the newly setspeed limit value. At Step S1512, if determining that it does not reach,the determination unit 901 goes forward to Step S1514. On the otherhand, at Step S1514, if determining that it has reached, thedetermination unit 901 goes forward to Step S1513.

At Step S1513, the determination unit 901 of the UI control unit 900determines that the terminating condition for the message for callingattention to acceleration is not satisfied, and goes back to Step S1402in FIG. 14. Also, at Step S1514, the determination unit 901 of the UIcontrol unit 900 determines that the terminating condition for themessage for calling attention to acceleration is satisfied, and goesback to Step S1402 in FIG. 14.

7. Summary

As clarified by the above description, the ECU for setting the speedlimit 120 according to the embodiment is configured

to determine whether there is a likelihood that the vehicle acceleratessteeply due to the switching of the speed limit value, based on thecondition for calling attention to acceleration, and

to display the message for calling attention to acceleration ifdetermining that there is a likelihood that the vehicle acceleratessteeply when the condition for calling attention to acceleration issatisfied.

Thus, the driver can recognize that there is a likelihood that behaviorof the vehicle may change (the vehicle accelerates steeply) when thespeed limit value is switched, due to the stepping amount on theaccelerator pedal by himself/herself, before the switching.

Consequently, the driver can adjust the stepping amount on theaccelerator pedal by himself/herself before the speed limit value isswitched, and safe traveling of the vehicle can be maintained when thespeed limit value is switched.

Third Embodiment

The second embodiment is configured to display the message for callingattention to acceleration so that behavior of the vehicle will notchange (the vehicle accelerates steeply) when the speed limit value isswitched. In contrast to this, the third embodiment is configured todisplay a message for calling attention to collision so that the vehiclewill not collide with a preceding vehicle due to behavioral change ofthe vehicle (the vehicle accelerates steeply) when the speed limit valueis switched. Note that a “preceding vehicle” may be a vehicle that istraveling ahead of the vehicle on the same lane, or may be a vehiclethat is traveling ahead of the vehicle on an adjacent lane, and isattempting to change into the same lane. In the following, the thirdembodiment will be described in detail, focusing on different pointsfrom the second embodiment.

1. Functions of UI Control Unit

First, functions of the UI control unit 1600 will be described accordingto the embodiment. FIG. 16 is a diagram that illustrates an example of afunctional configuration of the UI control unit 1600. As illustrated inFIG. 16, the UI control unit 1600 includes a current vehicle speeddisplay unit 501, a pedal-based vehicle speed display unit 502, adetermination unit 1601, a message output unit 1602, and a precedingvehicle speed calculation unit 1603. Among these, the current vehiclespeed display unit 501 and the pedal-based vehicle speed display unit502 have been described in the first embodiment, and their descriptionis omitted here.

The determination unit 1601 determines whether there is a likelihoodthat the vehicle accelerates steeply, and collides with a precedingvehicle when the speed limit setting unit 121 has set a candidate of thespeed limit value to be switched in the other ECU 140, and switches theupper limit speed value. Also, if determining that there is a likelihoodof collision, the determination unit 901 issues a command to the messageoutput unit 902 to display a “message for calling attention tocollision”.

To determine whether there is a likelihood that the vehicle collideswith a preceding vehicle, the determination unit 1601 determines, basedon the speed limit value currently set, the candidate of the speed limitvalue to be switched, the current vehicle speed, the pedal-based vehiclespeed, and the current vehicle speed of the preceding vehicle, whetherall of the following items of the “condition for calling attention tocollision” are satisfied:

the current vehicle speed is equivalent to the speed limit valuecurrently set;

the current pedal-based vehicle speed is greater than the currentvehicle speed;

the difference between the candidate of the speed limit value to beswitched and the speed limit value currently set is greater than orequal to a predetermined threshold;

the current pedal-based vehicle speed is greater than the currentvehicle speed of the preceding vehicle; and

the candidate of the speed limit value to be switched is greater thanthe current vehicle speed of the preceding vehicle.

Then, if determining that the condition for calling attention tocollision is satisfied, the determination unit 1601 issues a command tothe message output unit 1602 to display a “message for calling attentionto collision”.

Furthermore, in a state where the message for calling attention tocollision is being displayed, once the candidate of the speed limitvalue to be switched is transmitted to the other ECU 140, and the upperlimit speed value is switched, the determination unit 1601 determineswhether it is a timing to stop displaying the message for callingattention to collision, and issues a command to the message output unit1602. Specifically, the determination unit 901 issues a command to themessage output unit 1602 to stop displaying the “message for callingattention to collision” if determining that one of the following itemsof the “terminating condition for the message for calling attention tocollision” is satisfied:

the current pedal-based vehicle speed is less than or equal to thecurrent vehicle speed of the preceding vehicle, and is less than orequal to the newly set speed limit value; and

the current vehicle speed is less than or equal to the current vehiclespeed of the preceding vehicle, and has reached the newly set speedlimit value.

In response to a command to display the “message for calling attentionto collision” from the determination unit 1601, the message output unit1602 displays a predetermined message for calling attention to collisionon the speed display screen 600. Also, in response to a command to stopdisplaying the “message for calling attention to collision” from thedetermination unit 1601, the message output unit 1602 stops displayingthe message for calling attention to collision.

The preceding vehicle speed calculation unit 1603 determines whetherthere is a preceding vehicle, and if determining that there is apreceding vehicle, calculates the current vehicle speed of the precedingvehicle. Note that the current vehicle speed of the preceding vehiclemay be calculated based on temporal change of the distance to thepreceding vehicle (namely, the relative speed with respect to thevehicle), and the current vehicle speed of the vehicle where thedistance to the preceding vehicle is calculated, for example, based on ameasurement result of a separately provided sensor to measure thedistance to the preceding vehicle.

2. Display Examples of Speed Display Screen in Traveling Scenes

Next, display examples of the speed display screen 600 in travelingscenes will be described. FIG. 17 is a diagram that illustrates displayexamples of the speed display screen 600 in traveling scenes.

Specifically, the figure illustrates display examples of the speeddisplay screen 600 in traveling scenes in a case where travelling hasbeen started in a state where a speed limit value 711 of “60 km/h” hasbeen detected based on a road sign 701, and an upper limit speed valueof “60 km/h” has been set in the other ECU 140.

As illustrated in FIG. 17, the speed limit setting unit 121 detects aspeed limit value based on a road sign 702 at time T1, and stores acandidate of the speed limit value to be switched in the switchingcandidate storage unit 124. Once the speed limit setting unit 121 storesthe candidate of the speed limit value to be switched, the determinationunit 1601 determines whether there is a likelihood of a collision withthe preceding vehicle, by determining whether the condition for callingattention to collision is satisfied.

At time T1, the determination unit 901 determines that the condition forcalling attention to collision is satisfied because

the current vehicle speed 1720=“60 km/h” is equivalent to the speedlimit value currently set 711=“60 km/h”;

the current pedal-based vehicle speed 1721=“87 km/h” is greater than thecurrent vehicle speed 1720=“60 km/h”;

the difference=“20 km/h” between the candidate of the speed limit valueto be switched=“80 km/h” and the speed limit value currently set 711=“60km/h” is greater than or equal to a predetermined threshold;

the current pedal-based vehicle speed 1721=“87 km/h” is greater than thecurrent vehicle speed of the preceding vehicle 1730=“76 km/h”; and

the candidate of the speed limit value to be switched=“80 km/h” isgreater than the current vehicle speed of the preceding vehicle 1730=“76km/h”. Consequently, the message for calling attention to collision 1740is displayed on the speed display screen 600. Note that in the examplein FIG. 17, in response to the message for calling attention tocollision 1740 being displayed, the driver gradually decreases thestepping amount on the acceleration pedal 141 (the pedal-based vehiclespeed 1721 gradually decreases).

As illustrated in FIG. 17, at time T2, the vehicle passes by theposition where the road sign 702 is installed. When the vehicle passesby the position where the road sign 702 is installed, the speed limitsetting unit 121 transmits the candidate of the speed limit value to beswitched to the other ECU 140, and issues a command to set it as theupper limit speed value. Thus, the candidate of the speed limit value tobe switched (=“80 km/h”) is set, and the upper limit speed value isswitched.

After the upper limit speed value has been switched by the candidate ofthe speed limit value to be switched (=“80 km/h”), the message forcalling attention to collision is displayed on the speed display screen600 until the terminating condition for the message for callingattention to collision is satisfied.

At time T2, the determination unit 901 determines that the terminatingcondition for the message for calling attention to collision is notsatisfied because

the current pedal-based vehicle speed 1721=“85 km/h” is not less than orequal to the newly set speed limit value 711 (=“80 km/h”); and

the current vehicle speed 1720=“60 km/h” does not reach the newly setspeed limit value 711 (=“80 km/h”). Consequently, displaying the messagefor calling attention to collision 1740 on the speed display screen 600continues.

On the other hand, at time T3, the determination unit 901 determinesthat the terminating condition for the message for calling attention tocollision is satisfied because

the current pedal-based vehicle speed 1721=“75 km/h” is less than orequal to the newly set speed limit value 711 (=“80 km/h”). Consequently,displaying the message for calling attention to collision 1740 on thespeed display screen 600 ends.

Note that in the example in FIG. 17, at time T3, the current pedal-basedvehicle speed 1721 becomes equivalent to the current vehicle speed 1720,and thereafter, the vehicle speed is limited depending on the steppingamount on the acceleration pedal 141 by the driver. The current vehiclespeed 1720 after time T3 is roughly the same as the current vehiclespeed of the preceding vehicle 1730, and hence, the vehicle is unlikelyto collide with the preceding vehicle.

Note that in the example in FIG. 17, although the message for callingattention to collision 1740 is displayed to make the driver recognizethat there is a likelihood of collision with the preceding vehicle, thedisplay on the speed display screen 600 is not limited to the messagefor calling attention to collision 1740.

FIG. 18 is a diagram that illustrates another display example of thespeed display screen 600, to make the driver recognize that there is alikelihood of collision with the preceding vehicle. In FIG. 18, anindicator hand 1801 indicates the speed limit value to be newly set, andan indicator hand 1802 indicates the current vehicle speed of thepreceding vehicle. Also, an animation 1811 is a display for showing thatthere is a likelihood of collision with the preceding vehicle.

In this way, by contrastively displaying the speed limit value to benewly set along with the pedal-based vehicle speed, the driver canrecognize that the vehicle may accelerate steeply up to the speed limitvalue to be newly set. Also, by contrastively displaying the currentvehicle speed of the preceding vehicle along with the speed limit valueto be newly set, the driver can recognize that the current vehicle speedof the preceding vehicle is between the current vehicle speed of thevehicle and the speed limit value to be newly set, and there is alikelihood of collision with the preceding vehicle.

3. Flow of Process to Display the Pedal-Based Vehicle Speed

Next, a flow of a process to display the pedal-based vehicle speed bythe ECU for setting the speed limit 120, will be described. FIG. 19 andFIG. 20 constitute a flowchart that illustrates a flow of a process todisplay the pedal-based vehicle speed by the ECU fox setting the speedlimit 120. Note that substantially the same steps as the steps in theprocess to display the pedal-based vehicle speed described by using FIG.13 and FIG. 14 are assigned the same reference numbers, and theirdescription is omitted here.

Steps S1901 to S1905 in that FIG. 19 and Steps S2001 to S2005 in FIG. 20are different from FIG. 13 and FIG. 14. At Step S1901, the precedingvehicle speed calculation unit 1603 of the UI control unit 1600determines whether there is a preceding vehicle. At Step S1901, ifdetermining that there is no preceding vehicle, the determination unit901 goes forward to Step S806 in FIG. 20. On the other hand, at StepS1901, if determining that there is a preceding vehicle, thedetermination unit 901 goes forward to Step S1902.

At Step S1902, the preceding vehicle speed calculation unit 1603 of theUI control unit 1600 calculates the current vehicle speed of thepreceding vehicle. At Step S1903, the determination unit 1601 of the UIcontrol unit 1600 determines whether the condition for calling attentionto collision is satisfied. Note that a process to determine whether thecondition for calling attention to collision is satisfied that isexecuted by the determination unit 1601 of the UI control unit 1600 willbe described in detail later.

As a result of the process to determine whether the condition forcalling attention to collision is satisfied, if determining that thecondition for calling attention to collision is satisfied, thedetermination unit 901 goes forward to Step S1905 from Step S1904. AtStep S1905, the message output unit 1602 of the UI control unit 1600displays the message for calling attention to collision. After that, thedetermination unit 901 goes forward to Step S806 in FIG. 20.

On the other hand, at Step S1904, if determining that the condition forcalling attention to collision is not satisfied, the determination unit901 directly goes forward to Step S806 in FIG. 20.

At Step S2001 in FIG. 20, the determination unit 1601 of the UI controlunit 1600 determines whether the message for calling attention tocollision is currently displayed. If determining that the message forcalling attention to collision is not displayed, the determination unit1601 goes forward to Step S809. On the other hand, if determining thatthe message for calling attention to collision is currently displayed,the determination unit 1601 goes forward to Step S2002.

At Step S2002, the determination unit 1601 of the UI control unit 1600determines whether the terminating condition for the message for callingattention to collision is satisfied. Note that a process to determinewhether the terminating condition for the message for calling attentionto collision is satisfied will be described in detail later.

As a result of determination at Step S2002, if determining that theterminating condition for the message for calling attention to collisionis satisfied, the determination unit 1601 goes forward to Step S2004from Step S2003. At Step S2004, the determination unit 1601 of the UIcontrol unit 1600 deletes the candidate of the speed limit value to beswitched from the switching candidate storage unit 124. Thus, displayingthe message for calling attention to collision ends thereafter.

On the other hand, if determining that the terminating condition for themessage for calling attention to collision is not satisfied, thedetermination unit 1601 goes forward to Step S2005. At Step S2005, thedetermination unit 1601 of the UI control unit 1600 issues a command todisplay the message for calling attention to collision. Thus, themessage output unit 1602 of the UI control unit 1600 continues todisplay the message for calling attention to collision.

3. Flow of Process to Determine Whether the Condition for CallingAttention to Collision is Satisfied

Next, the process to determine whether the condition for callingattention to collision is satisfied (Step S1903) in the process todisplay the pedal-based vehicle speed, will be described in detail. FIG.21A is a flowchart that illustrates a flow of the process to determinewhether the condition for calling attention to collision is satisfied.

At Step S2101, the determination unit 1601 of the UI control unit 1600determines whether the current vehicle speed is equivalent to the speedlimit value currently set. At Step S2101, if determining that they arenot equivalent, the determination unit 1601 goes forward to Step S2107.On the other hand, at Step S2101, if determining that they areequivalent, the determination unit 1601 goes forward to Step S2102.

At Step S2102, the determination unit 1601 of the UI control unit 1600determines whether the current pedal-based vehicle speed is greater thanthe current vehicle speed. At Step S2102, if determining that it is notgreater, the determination unit 1601 goes forward to Step S2107. On theother hand, at Step S2102, if determining that it is greater, thedetermination unit 1601 goes forward to Step S2103.

At Step S2103, the determination unit 1601 of the UI control unit 1600determines whether the difference between the candidate of the speedlimit value to be switched and the speed limit value currently set isgreater than or equal to the predetermined threshold. At Step S2103, ifdetermining that it is less than the predetermined threshold, thedetermination unit 1601 goes forward to Step S2107. On the other hand,if determining that it is greater than or equal to the predeterminedthreshold, the determination unit 1601 goes forward to Step S2104.

At Step S2104, the determination unit 1601 of the UI control unit 1600determines whether the current pedal-based vehicle speed is greater thanthe current vehicle speed of the preceding vehicle. At Step S2104, ifdetermining that the current pedal-based vehicle speed is less than orequal to the current vehicle speed of the preceding vehicle, thedetermination unit 1601 goes forward to Step S2107. On the other hand,if determining that the current pedal-based vehicle speed is greaterthan the current vehicle speed of the preceding vehicle, thedetermination unit 1601 goes forward to Step S2105.

At Step S2105, the determination unit 1601 of the UI control unit 1600determines whether the candidate of the speed limit value to be switchedis greater than the current vehicle speed of the preceding vehicle. Ifdetermining that the candidate of the speed limit value to be switchedis less than or equal to the current vehicle speed of the precedingvehicle, the determination unit 1601 goes forward to Step S2107. On theother hand, if determining that the candidate of the speed limit valueto be switched is greater than the current vehicle speed of thepreceding vehicle, the determination unit 1601 goes forward to StepS2106.

At Step S2106, the determination unit 1601 of the UI control unit 1600determines that the condition for calling attention to collision issatisfied, and goes back to Step S1904 in FIG. 19. Also, at Step S2107,the determination unit 1601 of the UI control unit 1600 determines thatthe condition for calling attention to collision is not satisfied, andgoes back to Step S1904 in FIG. 19.

4. Details of Process to Determine Whether the Terminating Condition forCalling Attention to Collision is Satisfied

Next, the process to determine whether the terminating condition forcalling attention to collision is satisfied (Step S2001) in the processto display the pedal-based vehicle speed, will be described in detail.FIG. 21B is a flowchart that illustrates a flow of the process todetermine whether the terminating condition for calling attention tocollision is satisfied.

At Step S2111, the determination unit 1601 of the UI control unit 1600determines whether the current pedal-based vehicle speed is greater thanthe newly set speed limit value. At Step S2111, if determining that thecurrent pedal-based vehicle speed is less than or equal to the newly setspeed limit value, the determination unit 1601 goes forward to StepS2114. On the other hand, at Step S2111, if determining that the currentpedal-based vehicle speed is greater than the newly set speed limitvalue, the determination unit 1601 goes forward to Step S2112.

At Step S2112, the determination unit 1601 of the UI control unit 1600determines whether the current vehicle speed has reached the newly setspeed limit value. At Step S2112, if determining that it has not, thedetermination unit 1601 goes forward to Step S2113. On the other hand,at Step S2112, if determining that it has, the determination unit 1601goes forward to Step S2114.

At Step S2113, the determination unit 1601 of the UI control unit 1600determines that the terminating condition for the message for callingattention to acceleration is not satisfied, and goes back to Step S2002in FIG. 20. Also, at Step S2114, the determination unit 1601 of the UIcontrol unit 1600 determines that the terminating condition for themessage for calling attention to acceleration is satisfied, and goesback to Step S2002 in FIG. 20.

5. Summary

As clarified by the above description, the ECU for setting the speedlimit 120 according to the embodiment is configured

to determine whether there is a likelihood of a collision with thepreceding vehicle due to the switching of the speed limit value, basedon the condition for calling attention to collision, and

to display the message for calling attention to collision if determiningthat there is a likelihood of a collision with the preceding vehiclewhen the condition for calling collision to collision is satisfied.

Thus, the driver can recognize that there is a likelihood that thevehicle accelerates steeply, and may collide with the preceding vehiclewhen the speed limit value is switched, due to the stepping amount onthe accelerator pedal by himself/herself, before the switching.

Consequently, the driver can adjust the stepping amount on theaccelerator pedal by himself/herself before the speed limit value isswitched, and safe traveling of the vehicle can be maintained when thespeed limit value is switched.

Fourth Embodiment

In the first embodiment, a configuration is described that calculatesthe pedal-based vehicle speed and displays it on the speed displayscreen. Also, in the second embodiment, a configuration is describedthat calculates the pedal-based vehicle speed and displays it on thespeed display screen along with the message for calling attention toacceleration. Also, in the third embodiment, a configuration isdescribed that calculates the pedal-based vehicle speed and displays iton the speed display screen along with the message for calling attentionto collision.

However, it is obvious that these configurations may be arbitrarilycombined, or just one of these configurations may be included. Forexample, one may consider a configuration that calculates thepedal-based vehicle speed and displays it on the speed display screenalong with the message for calling attention to acceleration, and themessage for calling attention to collision.

Also, one may consider a configuration that does not display thepedal-based vehicle speed, but displays the message for callingattention to acceleration, and the message for calling attention tocollision. Alternatively, one may consider a configuration that does notdisplay the pedal-based vehicle speed, but displays one of the messagefor calling attention to acceleration, and the message for callingattention to collision.

Other Embodiments

In the first to fourth embodiments, the timing to switch the upper limitspeed value is a timing when the vehicle passes by the position where aroad sign is installed. However, the timing to switch the upper limitspeed value is not limited to that. For example, the upper limit speedvalue may be switched at a timing after a predetermined time has passedor the vehicle has traveled for a predetermined distance, since thevehicle had passed by the position where a road sign is installed.

Also, the second embodiment is configured to stop displaying the messagefor calling attention to acceleration when the terminating condition forthe message for calling attention to acceleration is satisfied after theupper limit speed value has been switched. However, the timing to stopdisplaying the message for calling attention to acceleration is notlimited to that. For example, displaying the message for callingattention to acceleration may be stopped at the timing when the upperlimit speed value is switched. Specifically, Step S1403 may be executedafter Step S807 in FIG. 14.

Similarly, the third embodiment is configured to stop displaying themessage for calling attention to collision when the terminatingcondition for the message for calling attention to collision issatisfied after the upper limit speed value has been switched. However,the timing to stop displaying the message for calling attention tocollision is not limited to that. For example, displaying the messagefor calling attention to collision may be stopped at the timing when theupper limit speed value is switched. Specifically, Step S2003 may beexecuted after Step S807 in FIG. 20.

Also, although displaying the speed limit value is not specificallymentioned in the first to fourth embodiments, the speed limit valuecurrently set may be displayed on the speed display screen. Also, in thefirst to fourth embodiments, although the pedal-based vehicle speed (orthe message for calling attention to acceleration and the message forcalling attention to collision) has been described to be displayed onthe speed display screen, it may be displayed elsewhere other than thespeed display screen.

Also, the second to fourth embodiments are configured to displayinformation derived from the pedal-based vehicle speed (the message forcalling attention to acceleration and the message for calling attentionto collision), in addition to displaying the pedal-based vehicle speedthat corresponds to the stepping amount on the acceleration pedal 141,on the speed display screen. However, they may be configured to displayinformation derived from the pedal-based vehicle speed (the message forcalling attention to acceleration and the message for calling attentionto collision), without displaying the pedal-based vehicle speed.

Also, although the second to fourth embodiments are configured todisplay the message for calling attention to acceleration and themessage for calling attention to collision on the speed display screen,they may be configured to have, for example, a sound output unit tooutput the messages as audio data via the sound output unit. Note thatif outputting audio data via the sound output unit, instead of themessages described above, predetermined alarm sounds may be output. Inother words, any unit may be used as long as it is capable of indicatinga likelihood of steep acceleration and/or collision to the driver.

Also, although the first to fourth embodiments are configured to detecta speed limit value on a road sign, based on image information obtainedby the imaging device 111, the method of detecting the speed limit valueis not limited to that, but a speed limit value may be detected anyother detection methods. As one of the other detection methods, forexample, a method may be considered that detects the speed limit valuespecified for a road for traveling depending on the positionalinformation of the vehicle where the speed limit value has been storedin advance in the navigation device 112.

Also, in the first to fourth embodiments, the description assumes thatthe upper limit speed value is set to the speed limit value specifiedfor a road for traveling. However, the upper limit speed value is notlimited to be set to the speed limit value specified for a road fortraveling, but, for example, may be set to a speed limit value specifiedby the driver.

Also, the first to fourth embodiments are configured to calculate thepedal-based vehicle speed that corresponds to the stepping amount on theacceleration pedal 141, and to display it on the speed display screen.However, the parameter displayed on the speed display screen is notlimited to the pedal-based vehicle speed as long as it is a parameterthat corresponds to the stepping amount on the acceleration pedal 141.As parameters that correspond to the stepping amount on the accelerationpedal 141 one may consider, for example, a parameter that represents anamount of operation by the driver such as the position of theacceleration pedal 141 and the pedaling force of the driver, and aparameter that represents the operational speed of the vehicle such asacceleration. Alternatively, one may consider a parameter thatrepresents the operational speed of a mechanism of the vehicle, such asthe rotational speed of the engine, the rotational speed of the motorfor driving, and the rotational speed of the tire. Alternatively, onemay consider a parameter that represents the amount of fuel consumptionsuch as the amount of gasoline consumption and the amount of powerconsumption of the motor for driving, and a parameter that represents astate of the power source, such as the opening of the engine throttleand the engine torque.

Also, although the first embodiment is configured to display thepedal-based vehicle speed on the speed display screen 600 all the time,but the pedal-based vehicle speed may be displayed on the speed displayscreen 600, for example, only when the candidate of the speed limitvalue to be switched is stored in the switching candidate storage unit124.

Also, the second to fourth embodiments are configured to determine thatthe vehicle is in a state where the vehicle speed is being limited to beless than or equal to the speed limit value if the current vehicle speedis equivalent to the speed limit value currently set, and the currentpedal-based vehicle speed is greater than the current vehicle speed.However, they may be configured to determine that the vehicle is in astate where the vehicle speed is being limited to be less than or equalto the speed limit value, by other methods. As an example, aconfiguration will be described in which the vehicle speed is limited tobe less than or equal to the speed limit value, by selecting a smallerdriving force among an upper limit driving force calculated from anupper limit acceleration that is allowed based on the difference betweenthe speed limit value and the current vehicle speed, and a driving forcerequested by the driver calculated from the stepping amount on theaccelerator pedal. In this case, in a state where the upper limitdriving force is selected, it is determined that the vehicle speed islimited to be less than or equal to the speed limit value. On the otherhand, in a state where the upper limit driving force is selected, it isdetermined that the vehicle speed is not limited to be less than orequal to the speed limit value.

Note that the present invention is not limited to the configurationsdescribed in the embodiments and those combined with the other elementshere. These can be changed within the scope of the present invention,and can be appropriately defined depending on usage.

The present application is based on and claims the benefit of priorityof Japanese Priority Application No. 2015-106826, filed on May 26, 2015,the entire contents of which are hereby incorporated by reference.

1. A vehicle speed limiter system, installed on a vehicle, comprising: adetection unit configured to detect a speed limit value of a road onwhich the vehicle is traveling; a setting unit configured to set thespeed limit value detected by the detection unit; a limiter unitconfigured to limit the vehicle speed of the vehicle, based on the speedlimit value set by the setting unit; an obtainment unit configured toobtain a stepping amount on an accelerator pedal of the vehicle; acalculation unit configured to calculate a parameter depending on thestepping amount, by using the stepping amount obtained by the obtainmentunit in a state where the vehicle speed of the vehicle is being limitedby the limiter unit; and a display unit configured to displayinformation based on the parameter calculated by the calculation unit,in a case where a speed limit value newly detected by the detection unitis greater than the speed limit value previously set by the settingunit, before the setting unit sets the speed limit value newly detected.2. The vehicle speed limiter system as claimed in claim 1, wherein thecalculation unit calculates the vehicle speed depending on the steppingamount, as the parameter, wherein the display unit displays the vehiclespeed calculated by the calculation unit, as the information.
 3. Thevehicle speed limiter system as claimed in claim 1, wherein thecalculation unit calculates the vehicle speed depending on the steppingamount, as the parameter, wherein the display unit displays informationrepresenting a change of behavior of the vehicle derived from thevehicle speed depending on the stepping amount, in a case where thespeed limit value newly detected is set, as the information.
 4. Thevehicle speed limiter system as claimed in claim 3, further comprising:a determination unit configured to determine whether the vehicleaccelerates by setting the speed limit value newly detected, based on acurrent vehicle speed of the vehicle, the vehicle speed depending on thestepping amount, the speed limit value previously set by the settingunit, and the speed limit value newly detected, wherein the display unitdisplays the information representing the change of behavior of thevehicle derived based on a determination result by the determinationunit.
 5. The vehicle speed limiter system as claimed in claim 3, furthercomprising: a vehicle speed calculation unit configured to calculate acurrent vehicle speed of a preceding vehicle ahead of the vehicle; and adetermination unit configured to determine whether there is a likelihoodthat the vehicle accelerates and the vehicle collides with the precedingvehicle, by setting the speed limit value newly detected, based on acurrent vehicle speed of the vehicle, the vehicle speed depending on thestepping amount, the speed limit value previously set by the settingunit, the speed limit value newly detected, and the current vehiclespeed of the preceding vehicle, wherein the display unit displays theinformation representing the change of behavior of the vehicle derivedbased on a determination result by the determination unit.